This invention is directed to a film formed from a two-component single resin including two components, not blended or co-polymerized, but inter-polymerized. A film formed from the resin has cross-direction extensibility at a low force, for example, between about 25% and about 50% at a force below 500 grams per 3 inches.
Films made from a blend of two components are typically known for maintaining the characteristics of both components as well as for their durability. However, such blended resins have a tendency to split apart after machine direction orientation. Another drawback to blended resins is that separate domains tend to form in a cross-directional gauge profile of the film, thereby resulting in non-uniform stretching of the film which can cause the tendency for the film to split apart.
Films made of a blend of linear low density resins and metallocene resins have improved durability and split resistance after machine direction orientation. However, in such a blend the domains may have a tendency to separate which could result in non-uniform stretching in the cross direction.
Two common types of film formulation approaches for making breathable films are a concentrate letdown approach and a fully compounded approach. In a concentrate letdown process, one resin is used as a carrier resin to make a concentrate with calcium carbonate or other fillers. The carrier resin, typically a high melt index/low viscosity resin, is used to disperse high loadings of filler. The concentrate is let down with another resin, typically a low melt index/high viscosity resin, to dilute the calcium carbonate to a desired percentage. Using two different resins in this manner can present difficulty in maintaining a desired component ratio in the film formulation when required for extensible attributes.
Conventional films require between about 550 and about 800 grams of force, or higher, per 3 inches to extend the film in a cross-direction by about 25% to about 50%. Although this is not an overwhelming amount of force, it is nevertheless desirable to have a film that can be stretched 25-50% in a cross-direction under considerably less force, particularly in such applications as diaper backsheets, training pant outer covers, and other absorbent garments that are designed to conform to a wearer's body. Better fit performance can be achieved through extensibility at a lower force.
There is thus a need or desire for a film formed from a resin having the attributes of two precursor resins, which has uniformity and thermal stability not typically achieved by blended polymers, and extensibility at a low force.
There is a further need or desire for a single resin that can be used to make breathable films in both a concentrate letdown approach and a fully compounded approach.